ABSTRACT Immune checkpoint blockade (ICB) aims to reactivate cytotoxic T-cell activities against tumors. Current ICB therapy has had a dramatic therapeutic impact, but only about 20% of patients have long-term tumor-free survival. A potential reason for the limited response rate is the lack of dominant neoantigens for T-cell recogni- tion. Several chemotherapeutic drugs have been identified as effective inducers of immunogenic cell death (ICD) and actively investigated in combination with ICB agents as off-label indications. However, a main chal- lenge in using chemotherapy as an ICD inducer is the dose-limiting side effects, including the toxicity to im- mune cells that will directly compromise cancer immunotherapy. In order to enhance ICB with ICD-inducing chemotherapy, a delivery system that specifically and efficiently affect tumor cells is necessary. With the ongo- ing R01 support (R01EB017791) we have developed nanoparticle (NP) systems with good circulation stability and high drug loading capacity that deliver more chemotherapeutic drugs to tumors and achieve greater anti- tumor efficacy relative to commercial benchmark products. We have also demonstrated that localized ionizing radiation (IR) further increased NP delivery to tumors. In this renewal application, we propose to use the NPs and IR to enhance their potential to induce ICD in tumors thereby sensitizing the tumors to ICB ther- apy. Our central hypothesis is that NPs will concentrate the drug in tumors without increasing systemic toxicity to induce ICD and help retain the released damage-associated molecular patterns and tumor antigens to gen- erate durable anti-tumor immune responses. We will combine NPs with high drug loading capacity and good circulation stability as well as surface modifiers that have contributed to in vivo performance of NPs in order to obtain optimal NPs for tumor delivery and intracellular uptake and retention. The activity of ICD-inducing NPs will be evaluated via the ability to promote anti-tumor immune responses (Aim 1); and their anti-cancer effect will be evaluated in combination with local ionizing radiation (Aim 2). To investigate the contribution of ICD-in- ducing NPs to ICB therapy, they will be combined with siRNA targeting PD-L1 or anti-PD-1/PD-L1 antibodies and evaluated in animal models of tumors with known (in)sensitivity to immunotherapy (Aim 3). The innovative aspect of this strategy is that it explores the untapped utility of NPs as a way of increasing the potential of chemotherapy to induce ICD and the role of carriers in cancer immunotherapy. With successful completion of this project, we expect to have developed a new therapeutic regimen with durable anti-cancer effects and high complete remission rates.